Application specific integrated circuitry for controlling analysis of a fluid

ABSTRACT

A circuit for determining characteristics of a fluid under-test is provided. The circuit includes analog-to-digital processing circuitry for interfacing with a sensor and host electronics. The analog-to-digital processing circuitry includes a frequency generator for providing stimulus to the sensor and receiving a response signal from the sensor. Conditioning circuitry for reducing analog signal offsets in the response signal and signal detection circuitry for identifying amplitude data of the response signal are provided. Further provided is analog-to-digital conversion circuitry for converting the detected amplitude data into digital form. Memory for holding calibration data and approximated fluid characteristics of the fluid under-test is included in the circuitry. The digital form of the response signal is processed in conjunction with the calibration data and approximated fluid characteristics to generate fluid characteristics of the actual fluid under-test.

CLAIM OF PRIORITY

This Application claims priority to U.S. Provisional Patent Application60/419,404, filed on Oct. 18, 2002, and entitled “Machine Fluid Sensorand Method,” which is incorporated by reference herein.

This U.S. Patent Application is also related to: (1) U.S. PatentApplication No. 60/456,517, filed Mar. 21, 2003, entitled “ResonatorSensor Assembly,” owned by the assignee of the present application andfiled on the same date; and (2) U.S. Patent Application No. 60/456,767filed, Mar. 21, 2003, entitled “Mechanical Resonator,” owned by theassignee of the present application and filed on the same date.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to fluid sensors, and moreparticularly to specialized circuitry for interfacing with a fluidsensor to enable control and monitoring of the fluid sensor to generatecharacterizing data for a fluid.

2. Description of the Related Art

In the art of fluid analysis, there exists a number of techniques fordetermining the characteristics of a fluid. In the case of fluids usedin machines, such as automobiles, engines, and the like, there has beenmuch experimentation in fluid analysis. For instance, a machine commonlyrequires specific fluids, and some are used to lubricate components ofthe machine. As is well known, one such fluid is engine oil, which isused to lubricate critical parts that would otherwise be damaged due totheir continuous frictional movement.

To understand the state of a fluid at a particular point in time,sensors have been used to quantify characteristics of the fluid. Suchsensors have included the use of resonating quartz-type sensors. Thestudy of quartz-type sensors in the analysis of fluids, such as engineoil, has taken on many different avenues. The sensors come in all typesof shapes, sizes, textures, operating frequency, etc. Depending on thecharacteristics targeted for sensing, the sensors are either shaped in aparticular geometric design, coated with chemical layers, or arranged inarrays. Although prior art sensing techniques have taken on a wide arrayof forms, fluid sensing devices have largely been tested in a laboratorysetting. In such a setting, the sensors can be connected to laboratoryequipment to provide the necessary stimulus and detect the output fromthe sensor. The output from the sensor can be analyzed by the operatoror caused to be processed by other computer programs to enable a user todetermine whether or not the sensor detected appropriate data. Ifappropriate data is being generated, the data can be further interpretedto ascertain fluid characteristics.

As can be appreciated, this process, although computer assisted, iscumbersome and time consuming. Therefore, currently sensing technology,although able to sense some fluid characteristics, may not suffice in acommercial environment where on-the-fly or real-time in-situmeasurements, analysis and feedback is needed. Such commercialapplications may include, for instance, oil sensing applications. Asmentioned above, such oil sensing applications can include, for example,engine oil sensing, oil drilling equipment sensors, and otherapplications where a fluid's characteristics need to be monitored andanalyzed.

In view of the foregoing, there remains a need in the art for improvedsensing methods and systems for analyzing fluids. In particular, thereremains a need for specialized circuitry for interfacing with a sensorto enable control, receipt of sensed data, and processing of the senseddata to rapidly provide characterizing data for the fluid being sensed.

SUMMARY OF THE INVENTION

Broadly speaking, system and method is provided for monitoring qualityparameters and level of a fluid used in the lubrication of a machine,such as a vehicle. In one aspect of the invention, a system and methodis provided for determining the characteristics of a known machinefluid, and more specifically for monitoring the condition of alubricant, e.g., engine oil. The present invention defines acommunication interface between the sensor and the machine in which thefluid is to be monitored. In one embodiment, the communication interfaceis defined by an application specific integrated circuit (ASIC). TheASIC, in broad terms, incorporates circuitry for communicating with thesensor to initiate sensor activity, receive sensor output, process thesensor output, and communicate the sensor output to a user interface forpresentation.

In one embodiment, a system for sensing characteristics of a fluid isdisclosed. The system includes a tuning fork that is at least partiallysubmerged in a fluid under-test and an application specific integratedcircuit (ASIC). The ASIC includes analog input/output circuitry forproviding stimulus to the tuning fork and receiving a response signalfrom the tuning fork. Conditioning circuitry for reducing analog signaloffsets in the response signal and signal detection circuitry foridentifying phase and amplitude data of the response signal are furtherprovided as part of the ASIC. The ASIC further includesanalog-to-digital conversion circuitry for converting the detected phaseand amplitude data into digital form. Memory for holding calibrationdata and approximated fluid characteristics of the fluid under-test isintegrated in the ASIC, wherein the digital form of the response signalis processed in conjunction with the calibration data and approximatedfluid characteristics to generate fluid characteristics of the fluidunder-test.

In another embodiment, a circuit for determining characteristics of afluid under-test is provided. The circuit includes analog-to-digitalprocessing circuitry for interfacing with a sensor and host electronics.The analog-to-digital processing circuitry includes a frequencygenerator for providing stimulus to the sensor and receiving a responsesignal from the sensor. Conditioning circuitry for reducing analogsignal offsets in the response signal and signal detection circuitry foridentifying phase and amplitude data of the response signal areprovided. Further provided is analog-to-digital conversion circuitry forconverting the detected phase and amplitude data into digital form.Memory for holding calibration data and approximated fluidcharacteristics of the fluid under-test is included in the circuitry.The digital form of the response signal is processed in conjunction withthe calibration data and approximated fluid characteristics to generatefluid characteristics of the actual fluid under-test.

In yet another embodiment, a method for interfacing with a mechanicalsensor to obtain characteristics of a fluid under-test is disclosed. Themechanical sensor is at least partially submerged in the fluidunder-test. The method includes applying a variable frequency signal tothe sensor and receiving a frequency response from the sensor. Thefrequency response is conditioned and components of the frequencyresponse are detected. The method further includes converting thefrequency response to digital form, such that the digital form isrepresentative of the frequency response received from the sensor. Then,first calibration variables are fetched from memory. As used herein, theterm “fetch” should be understood to include any method or techniqueused for obtaining data from a memory device. Depending on theparticular type of memory, the addressing will be tailored to allowaccess of the particular stored data of interest. The first calibrationvariables define physical characteristics of the sensor. Secondcalibration variables are fetched from memory. The second calibrationvariables define characteristics of the sensor in a known fluid. Thedigital form is then processed when the sensor is in the fluidunder-test, the processing uses the fetched first and second calibrationvariables to implement a fitting algorithm to produce fluidcharacteristics of the fluid under-test.

In still another embodiment, a method for interfacing with a tuning forkto obtain characteristics of a fluid under-test is disclosed. The tuningfork is configured to be at least partially submerged in the fluidunder-test. The method includes applying a variable frequency signal tothe tuning fork and receiving a frequency response from the tuning fork.The method also includes conditioning the frequency response, detectingsignal components of the frequency response, and converting thefrequency response to digital form. The digital form beingrepresentative of the frequency response received from the tuning fork.Then, the method fetches calibration variables for the tuning fork andprocessing the digital form of the response received from the tuningfork when in the fluid under-test, the processing being performed alongwith the fetched calibration variables and implementing a fittingalgorithm to produce fluid characteristics of the fluid under-test.

In another embodiment, an application specific circuit (ASIC) forprocessing signals used to determine characteristics of a fluidunder-test is disclosed. The ASIC is in communication with a tuning forkdesigned to operate a frequency that is less than 100 kHz. The ASICincludes circuitry for communicating a frequency signal to the tuningfork, circuitry for processing the a response signal received from thetuning fork into digital form, circuitry for storing calibration datafor the tuning fork; circuitry for executing a fitting algorithm toascertain characteristics of the fluid-under-test (the executingutilizing the calibration data); and circuitry for interfacing the ASICcircuitry that is external to the ASIC.

In summary, the present invention provides a sensing system thatincludes a mechanical resonator sensor and an ASIC that is employed formonitoring the level, condition, or both of a fluid. The sensing systemis configured to include an input signal generator for exciting amechanical resonator sensor, an ASIC for obtaining an output signal thatcorresponds with the response of the resonator to the input signal inthe presence of a fluid during fluid monitoring. The sensing system maybe further configured (e.g. as part of the ASIC or separate from it) toinclude a signal conditioner having at least one signal modifier forreceiving the output signal, forming a conditioned signal in responsethereto, and communicating the conditioned signal to a microprocessorunit. Though the signal generator, receiver and signal conditionerfunctions may be integrated into fewer components, divided amongadditional components, or split among a plurality of substrates, in apreferred embodiment, the functions are all performed by an assembly ona common substrate, namely a common integrated circuit.

As can be appreciated from the above, the present invention thus alsocontemplates a method for monitoring a machine fluid including theoperations of placing a sensor including a mechanical resonator into afluid reservoir, passageway, circulation system, resonating the sensorwith an input signal while the resonator is in the reservoir, passage orcirculation system, receiving an output signal from the sensorindicative of the response of the resonator to the fluid and the inputsignal, conditioning the output signal, and communicating the outputsignal to a processor. Optionally, a visual or audible indicator istriggered as a result of the output signal.

Other aspects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings.

FIG. 1A-1 illustrates a fluid sensing system, in accordance with oneembodiment of the present invention.

FIG. 1A-2 illustrates another embodiment of the present invention, wherethe tuning fork is contained within a closed environment to ensureconsistent measurement of a fluid under-test.

FIG. 1B illustrates an exemplary automobile incorporating the fluidsensing system, in accordance with one embodiment of the presentinvention.

FIGS. 1C-1E provide further illustrative examples in which the fluidsensing system of the present invention can be used.

FIG. 2A illustrates a block diagram of an ASIC designed to providestimulus to a tuning fork and receive and process data to provideinformation regarding the characteristics of a fluid under-test.

FIG. 2B illustrates an example where a digital processor is outside ofthe ASIC, in accordance with one embodiment of the present invention.

FIG. 2C illustrates another detailed block diagram of the ASIC, inaccordance with one embodiment of the present invention.

FIGS. 2D and 2E provide exemplary data that may be stored in the ASIC'smemory, in accordance with one embodiment of the present invention.

FIGS. 3A through 3D illustrate the flexibility of the component blocksthat may be integrated in the ASIC, in accordance with one embodiment ofthe present invention.

FIG. 4 illustrates a circuit diagram for a tuning fork equivalentcircuit and a read-out input impedance circuit, in accordance with oneembodiment of the present invention.

FIG. 5 is a graph that plots voltage (Vout) versus frequency (ω), toillustrate a typical resonant frequency response, in accordance with oneembodiment of the present invention.

FIGS. 6A-6D illustrate exemplary techniques for conditioning the signalreceived from the tuning fork, in accordance with one embodiment of thepresent invention.

FIG. 7 illustrates the tuning fork with an integrated capacitor, inaccordance with one embodiment of the present invention.

FIG. 8 is a flow chart diagram depicting method operations performed tocalculate calibration data for a tuning fork, in accordance with oneembodiment of the present invention.

FIG. 9 is a flow chart diagram depicting method operations forcontrolling signals to a tuning fork, and receiving and processingsignals in an ASIC to determine characteristics of a fluid under-test,in accordance with one embodiment of the present invention.

FIG. 10 is a flow chart diagram depicting method operations forexecuting a fitting algorithm, in accordance with one embodiment of thepresent invention.

FIGS. 11A-11C illustrate plots for calibration and actual examination ofa fluid under-test, in accordance with one embodiment of the presentinvention.

FIG. 12 illustrates a flow chart diagram depicting processing operationsperformed to determine characteristics of a fluid under-test, inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention is disclosed for an application specific integrated circuit(ASIC) that is used to interface with a fluid sensor to determinecharacteristic conditions of the fluid being sensed. As used herein, thefluid being sensed will be referred to as a “fluid under-test.” Althoughspecifics are provided with regard to engine oil, as the fluidunder-test, it should be understood that any fluid capable of beingsensed to ascertain its characteristics (e.g., chemical components orphysical attributes) can utilize the teachings defined herein. Forinstance, the term “fluid” should be broadly construed to included anymaterial in either a liquid form, gas form, a solid form, or acombination of any one of liquid, gas or solid.

Accordingly, in the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps have notbeen described in detail in order not to unnecessarily obscure thepresent invention.

Generally, the present invention provides a versatile fluid sensingsystem. More specifically, the present invention provides a fluidsensing system for machines that rely upon the presence, condition orboth of a fluid to maintain efficient operation, such as (withoutlimitation) a synthetic or natural engine oil. In an automotiveapplication, the user is provided with the ability to determine theactual condition (e.g. or the relative deviation of the state of theengine oil from its initial or virgin state) of the engine oil at anyparticular time, including during operation. Alternatively, inconjunction with assessing fluid condition, the present invention mayalso be used to determine the amount of fluid remaining in a reserve ofan assembly. This advantageously allows machine operators to extend theduration between fluid service events, while helping to assure continuedoperational integrity of a machine. Any dynamic assembly that depends onfluids to operate (e.g., where friction and heat are of a concern), willbenefit from a system capable sensing the state of a fluid. Forinstance, the ability to dynamically monitor fluid condition, processdata obtained from the monitoring, and report characteristics of thefluid to an interface or operator can have many applications. Assembliesthat may benefit from the defined embodiments of the present inventionare many, and can include without limitation, engines in general,automobiles, heavy machinery, military equipment, airplane parts,measurement while drilling, logging while drilling, exploration andproduction well logging tools, marine transportation, sub-seaexploration and aerospace related equipment, or any other fluidcontaining application. Still further, the fluid may be in a fluidrefinery container, a fluid pipeline, or be the subject of testing andanalysis. In one example, the fluid under-test may also be the subjectof liquid chromatography.

In the automotive field, numerous components require lubrication, whichis not limited to engine oil. For example, other automotive componentsmay include the transmission, the transfer case, the differential, etc.Still further, the sensing system may further be used to determined thequality and amount of other fluids which are not necessarily usedpredominantly as a lubricant, including: brake fluids, steering fluids,antifreeze fluids, refrigerant fluids, windshield washer fluids, or anyother fluid located in an automotive system.

In one embodiment, an oil sensing system is disclosed to determine thecomponent characteristics and amount of engine oil. In an automotiveapplication, the oil sensing system will provide a user, at a minimum,with a warning as to the need to change the oil (such as owing to thepresence of contaminants, a breakdown or loss of useful ingredients orotherwise). In such an application, the warning is essentially informingthe user of the automobile that the engine oil has reaches a qualitylevel or condition that is lower than that recommend by the automobile'smanufacturer (or set by the oil manufacturer).

The fluid sensing system preferably uses a mechanical resonator as thefluid sensor. The mechanical resonator is at least partially containedin the fluid under-test. To monitor the condition of the fluidunder-test (i.e., engine oil), the mechanical resonator is provided withelectrical energy through a frequency generator. The frequency generatoris designed to apply a frequency signal (to the mechanical resonator)that is swept over a predetermined frequency range. Electronics are thenused to detect the response signal from the mechanical resonator andprocess the signal to ascertain characteristics of the fluid under-test.In an embodiment of the present invention, the electronics are providedin the form of an application specific integrated circuit (ASIC).

FIG. 1A-1 illustrates a fluid sensing system 110, in accordance with oneembodiment of the present invention. The fluid sensing system 110utilizes a tuning fork 116 which can be placed into a fluid under-test114. In simplest terms, the fluid may reside in a container 112. Thecontainer 112 can take on any form, such as a closed form, open form,pressurized form, etc., so long as it can hold the desired fluid. In aspecific example, the fluid under-test 114 is engine oil. As shown, thetuning fork 116 is closely coupled to a temperature sensor 117 whichprovides feedback to electronics of the fluid sensing system 110. Forexample, the temperature sensor 117 may be a resistance temperaturedetector (RTD), or any other suitable temperature monitoring device. Asensor control and processing circuit 118 provides stimulus (e.g., suchas an applied frequency) via connection 111 b to the tuning fork 116.The response from the tuning fork 116 is received via connection 111 aback to the sensor control and processing circuit 118. The response isan analog response of the tuning fork 116.

In one embodiment, the temperature sensor 117 is further interfaced viaconnection 111 c to the sensor control and processing circuit 118. Inspecific embodiments, the connection 111 c will also provide temperaturedata back to the local machine electronics 120. The connections 111 areprovided to illustrate a functional interconnect between the tuning fork116 and the temperature sensor 117, although it should be understoodthat fewer or more physical wires or connections may be used to completethe electrical interconnections. The local machine electrics 120 may be,for example, electronics of a machine containing the fluid under-test114. In the automobile industry, specialized computers and electronicare commonly provided as native to an automobile, and such electronicsand associated software operate to control and receive feedback from thevarious systems of the automobile. Accordingly, it is envisioned thatthe local machine electronics 122 can also make use of temperature data.

The temperature sensor 117 therefore will provide temperature data forthe fluid under-test in a location that is closely coupled to the tuningfork 116, so that an accurate temperature near the tuning fork 116 canbe obtained. The sensor control and processing circuit 118 may then usethe temperature obtained from the temperature sensor 117 to process thesignals.

Further, as the local machine electronics will receive the dataprocessed by the sensor control and processing circuit 118, appropriateread-out to local machine user interface 122 can be made. Local machineuser interface 122 may be a display on an automobile, may be a displayon a read-out of a machine (analog or digital display), or may be adisplay of a computer that is local to the machine containing the fluidunder-test 114.

Broadly speaking, the sensor control and processing circuit 118 isprovided as circuitry that closely communicates with the tuning fork 116to provide stimulus to the tuning fork, and also receive the responsefrom the tuning fork and process the data received from the tuning forkinto appropriate forms to be further processed by the local machineelectronics 120. In a preferred embodiment, the sensor control andprocessing circuit 118 is provided in the form of anapplication-specific integrated circuit (ASIC). Accordingly, the localmachine electronics 120 will be interchangeably referred to herein asthe “ASIC 118.”

In one embodiment, the ASIC 118 has the capability of generating afrequency signal that is provided through 111 b to the tuning fork, andthen is capable of receiving analog signals from the tuning fork over111 a. The analog signals received over 111 a are then processed by theASIC to extract information that will be used to identifycharacteristics of the fluid under-test 114. In one embodiment, theanalog data is conditioned by the ASIC and then converted into digitalform before being passed to the local machine electronics 120. Localmachine electronics 120 will then communicate the detectedcharacteristics of the fluid under-test to the local machine userinterface 122.

FIG. 1A-2 illustrates another embodiment, where the tuning fork ismaintained in a closed environment 125 that will contain an amount ofthe fluid under-test 114 a. As the condition of the fluid under-testfluctuates during operation of a motor, for example, it may be desirousto take in a sample 114 a of the fluid under-test 114 and place it in aseparate compartment that is maintained at a substantially constanttemperature. To maintain the temperature at a particular level, atemperature controller 125 a (e.g., a heating coil, a cooling system,etc.) can be used. The temperature controller 125 a will thus maintainthe temperature of the sample fluid under-test 114 a consistently at agiven temperature, which may be different than the fluid under-test 114contained in the container 112 (e.g., oil pan of a motor). Thetemperature controller 125 a can either operate alone, or can becontrolled through a circuit or software. In one embodiment, thetemperature controller 125 a is coupled to the ASIC 118, which willinclude circuitry or firmware that will monitor the temperature andadjust the temperature as needed. In still another embodiment, thetemperature controller 125 a can be desired to lower the temperaturefluctuation range, as opposed to allowing the fluid 114 a to shiftacross the entire temperature spectrum of the entire fluid under-test114.

FIG. 1B illustrates an automobile 113 having an engine 113 a and adisplay dashboard 113 b. The engine 113 a will include an oil pan 113 c,as is well known in the art. The oil pan 113 c will have a tuning fork116 inserted therein. The tuning fork 116 may be inserted at anylocation within the oil pan 113 c, so long as the tuning fork tines aresufficiently in contact with the fluid under-test 114. The fluidunder-test 114 is the oil contained within the oil pan 113 c, in thisexample. The tuning fork 116 is shown coupled to the ASIC 118, in oneembodiment.

The ASIC 118 is in turn coupled to the local machine electronics 120that may be provided by the automobile 113 manufacturer. In operation,the tuning fork 116 will be contained within the oil pan 113 c and theASIC 118 will be integral with the tuning fork 116. In anotherembodiment, the ASIC will be located close to the tuning fork 116, butnot integral therewith. In still another embodiment, the ASIC will bemounted to a printed circuit board that is connected to the automobile113 (i.e., either with other local electronics or separate there from).

Irrespective of its physical installation, the ASIC 118 may continuouslymonitor the condition of the fluid under-test 114 and provide data tothe ASIC 118. The ASIC 118 will therefore continuously communicate backto the local machine electronics 120 which then provides the informationto the local machine user interface 122. In another embodiment, themonitoring will only be during a specific duration, at predeterminedtimes, or on-demand (i.e., per user/technician request or query). Inthis example, the local machine user interface 122 will be provided inthe form of a display dashboard 113 b that provides visual, audible, ora combination of visual and audible information to a driver or user ofthe automobile 113. In this manner, the driver (or technician) of theautomobile 113 will be informed of the condition of the fluid under-test114 during the use/service of the automobile 113. In one example, whenthe fluid under-test, e.g., engine oil, becomes degraded to a level thatmay require replacement, the local machine user interface 122 willdisplay an indication to the user of the automobile 113 by way of thedisplay dashboard 113 b.

In one arrangement, the tuning fork 116 may be a part of an oil drainplug. In this arrangement, the oil sensing system may be furtherconfigured with an actuator, sensor or combination thereof (e.g.,magnetic sensor) that indicates if the tuning fork 116 (and hence theoil drain plug) has been placed in the oil drain hole. Such an indicatoris particularly attractive to the extent that the insertion or removaland re-insertion of an oil drain plug typically coincides with thefilling of or removal and re-filling of fluid from the engine. In thismanner, the ability to provide a reference value for further comparisonis readily enhanced. That is, upon insertion of the drain plug in thedrain hole, the actuator, sensor or combination thereof will send asignal that effectively re-sets the system. As a result, A measurementcan be taken of the fluid immediately upon its filling, which isexpected to generally coincide with insertion of the drain plug, and areference value established for the fluid (i.e., the fluid in its freshstate), which can be stored in memory associated with the system forlater comparison.

FIG. 1C illustrates an example where the ASIC 118 is connected to thetuning fork 116 and the temperature sensor 117 in a laboratory setting(or on a desktop where a fluid needs to be tested to identify its fluidcharacteristics). The fluid under-test 114 can then be analyzed usingthe ASIC 118 and a computer system. Still further, the ASIC 118 can beintegrated onto a host card that can be installed onto the computer,using a standard bus interface (i.e., parallel bus, USB, IDE, SCSI,etc.). In another embodiment, a computer can be specifically integratedwith the ASIC 118 so that a host card need not be installed onto thecomputer. In that situation, the tuning fork 116 and the temperaturesensor 117 would be connected directly to the computer system and thecomputer system would provide the processing necessary to determine thecharacteristics of the fluid under-test 114. In still anotherembodiment, the ASIC 118 can be integrated into a handheld or portabledevice. Such a portable device can have many applications, such aslaboratory applications, filed applications, factory applications, etc.

In yet another embodiment, FIG. 1C illustrates a laboratory settingwhere a computer is connected to the tuning fork 116 and the ASIC 118 isintegrated with the tuning fork 116. The temperature sensor 117, in asimilar manner, would be integrated closely to the tuning fork 116 sothat appropriate temperature readings can be obtained near the tuningfork 116. In still another embodiment, the tuning fork 116, andtemperature sensor 117 can be integrated with the ASIC 118 at a remotepoint in order to obtain fluid characteristic data from a fluidunder-test 114. For instance, in an oil exploration site 115 of FIG. 1E,the tuning fork/ASIC can be used to identify the characteristics of oilthat is intended for drilling. In a further example, the tuningfork/ASIC can be integrated directly into standard measurement whiledrilling, logging while drilling, exploration and production welllogging tools, so that physical characteristics of oil and/or gasquality can be determined on-the-fly, as formation fluid is being pumpedfrom a well. The results can then be provide back to a computer, such asa laptop computer (or a local measurement while drilling, logging whiledrilling, exploration and production well logging tool computerdisplay), to provide instant information regarding physicalcharacteristics of the oil or gas in and from the formation.

FIG. 2A illustrates a block diagram of the ASIC 118 and its componentsdesigned to provide stimulus to the tuning fork 116 and receive andprocess data to provide information regarding the characteristics of afluid under-test. In one embodiment, the ASIC will include a frequencygenerator 130 that is configured to provide a frequency stimulus to thetuning fork 116 by way of communication line 156. The generatedfrequency is preferably a variable frequency input signal, such as asinusoidal wave or square wave, that sweeps over a predeterminedfrequency range. The sweeping range will preferably include theresonance frequency range of the sensor. Preferably, the frequency isless than 100 kHz, and more preferably, is in the range of about 5 kHzand about 50 kHz, and most preferably, is in the range of about 20 kHzto about 35 kHz.

The tuning fork response over the frequency range is then monitored todetermine the physical and electrical properties of the fluidunder-test. The response from the tuning fork 116 is provided to asignal conditioning circuitry block 132, by way of a communication line158. In one preferred embodiment, the tuning fork 116 will also includea capacitor 316, which will be described in greater detail below. Thecapacitor 316 is also coupled to the signal conditioning circuitry 132.The signal conditioning circuitry 132 is provided to receive the analogform of the signal from the tuning fork 116 and condition it so thatmore efficient signal processing may be performed before furtherprocessing.

The signal conditioning circuitry 132 will receive the analog outputfrom the tuning fork 116, and is designed to substantially eliminate orreduce signal offsets, thus increasing the dynamic range of the signalthat is to be further processed. In this manner, further processing canconcentrate on the signal itself as opposed to data associated with thesignal offset.

Signal detection circuitry (SDC) 134 is also provided, and it is coupledto the signal conditioning circuitry 132. Signal detection circuitry 134will include, in one embodiment, a root mean squared (RMS) to DCconverter, that is designed to generate a DC output (i.e., amplitudeonly) equal to the RMS value of any input received from the signalconditioning circuitry 132. The functional operation of a RMS-to-DCconverter is well known to those skilled in the art. In anotherembodiment, the signal detection circuitry 134 may be provided in theform of a synchronous detector. As is well known, synchronous detectorsare designed to identify a signal's phase and amplitude whenpreprocessing of an analog signal is desired in order to convert theanalog signal into digital form. Once the signal detection circuitryblock 134 processes the signal received from the signal conditioningcircuitry 132, the signal detection circuitry 134 will pass the data toan analog-to-digital converter (ADC) 136. The analog-to-digitalconverter 136 will preferably operate at a sampling rate of up to 10 kHzwhile using a 10-bit resolution. The analog-to-digital converter (ADC)can, of course, take on any sampling rate and provide any bit resolutiondesired so long as the data received from the signal detection circuitryis processed into digital form.

The ADC 136 will also receive information from the temperature sensor117 to make adjustments to the conversion from the analog form to thedigital form in view of the actual temperature in the fluid under-test114. In an alternative embodiment, the temperature sensor 117 can beomitted, however, the temperature sensor 117 will assist in providingdata that will expedite the processing by the ASIC 118.

The digital signal provided by the analog-to-digital converter 136 isthen forwarded to a digital processor 138. The digital processor 138 iscoupled to memory storage 140 by way of a data bus 150 and a logic bus152. Logic bus 152 is also shown connected to each of the frequencygenerator 130, the signal conditioning circuitry 132, the signaldetection circuitry 134, and the analog-to-digital converter 136. Adigital logic control 142 is directly coupled to the logic bus 152. Thedigital logic control 142 will thus communicate with each of the blocksof the ASIC 118 to synchronize when operation should take place by eachone of the blocks. Returning to the digital processor 138, the digitalprocessor 138 will receive the sensed data from the tuning fork 116 indigital form, and then apply an algorithm to identify characteristics ofthe fluid under-test 114.

The algorithm is designed to quickly identify variables that are unknownin the fluid under-test. The unknown variables may include, for example,density, viscosity, the dielectric constant, and other variables (ifneeded, and depending on the fluid). Further, depending on the fluidunder-test 114 being examined, the memory storage 140 will have adatabase of known variables for specific calibrated tuning forks. In oneembodiment, the memory storage 140 may also hold variables forapproximation of variables associated with particular fluids. In anotherembodiment, the memory storage 140 will store serial numbers (or sometype of identifier) to allow particular sets of data to be associatedwith particular tuning forks. In such a serial number configuration, thestorage memory can hold unique data sets for a multitude of uniquetuning forks. When a tuning fork is sold, for example, the purchaserneed only input its assigned serial number into an interface, and thedata set associated for that tuning fork will be used during operation.From time to time, it may be necessary to upload additional data sets tothe storage memory 140, as new tuning forks (with unique serial numbers)are manufactured.

The process for using variable data from prior calibrations and fromfluids that may closely resemble the fluid under-test, will be describedin greater detail below. In general, however, the digital processor 138may quickly access the data from the memory storage 140, and digitallyprocess an algorithm that will generate and output variables that definethe fluid under-test 114.

The digital processor will then communicate through the digital logiccontrol 142 and communication line 154, the identified variables thatcharacterize the fluid under-test 114 to the local machine electronics120 (or some recipient computer, either locally or over a network). Inone embodiment, the local machine electronics 120 will include an enginecontrol unit (ECU) 121, that directly receives the data from the digitallogic control 142 through signal 154. The engine control unit 121 willthen receive that data and, in accordance with its programmed routines,provide feedback to the local machine user interface 122.

For example, the engine control unit 121, may set a different thresholdfor when the fluid under-test 114 (i.e., engine oil), has degraded. Forexample, different car manufacturers, and therefore, different enginecontrol units for each car will define a particular viscosity, densityand dielectric constant (or one or a combination thereof) that may beindicative of a need to change the oil. However, this programmablethreshold level setting will differ among cars. Thus, the engine controlunit 121 will provide the local machine user interface 122 theappropriate signals depending on the programming of the particularautomobile or engine in which the engine control unit 121 is resident.

The ASIC 118 has been shown to include a number of component blocks,however, it should be understood that not all components need beincluded in the ASIC as will be discussed below. In this example, thedigital processor 138 may be physically outside of the ASIC 118, andrepresented in terms of a general processor. If the digital processor138 is located outside of the ASIC 118, the digital logic control 142will take the form of glue logic that will be able to communicatebetween the digital processor 138 that is located outside of the ASIC118, and the remaining components within the ASIC 118. In the automobileexample, if the processor 138 is outside of the ASIC, the processor willstill be in communication with the engine control unit 121.

FIG. 2B illustrates an example when the digital processor 138 is outsideof the ASIC 118. In such an embodiment, the digital processor 138 may beintegrated into a printed circuit board that is alongside of the ASIC118, or on a separate printed circuit board. In either case, the ASIC118 will be in communication with the tuning fork 116 to providestimulus and to process the received analog signals from the tuning fork116. The ASIC will therefore convert the analog signals coming from thetuning fork 116 and convert them to a digital form before being passedto the digital processor 138.

If the ASIC 118 is provided on an automobile, and the digital processor138 is outside of the ASIC 118, the digital processor 138 will still beable to communicate with the engine control unit 121 of the localmachine electronics 120. The engine control unit 121 will thereforecommunicate with the local machine user interface 122. In this example,the user interface may include a user display 122 b. The user display122 b may include analog and digital indicators 122 d. The analog anddigital indicators 122 d may indicate the qualities of the fluidunder-test (e.g., engine oil), and can be displayed in terms of a gaugereading to indicate to the user when the fluid under-test has degradedor needs to be changed.

In another embodiment, the user display 122 b may include a digitaldisplay 122 c (e.g., monitor) that may provide a digital output ordisplay of the condition of the engine oil to the user through anappropriate graphical user interface (GUI). The user interface 122 mayalso include a user input 122 a. The user input 112 a may be aelectronic interface that would allow a service technician, for example,to provide updated calibration information for a tuning fork that isinserted in a particular vehicle, or provide adjusted approximations fornew engine oils that may just have come onto the market.

By way of the user input 122 a, a service technician will be able toinput new data to the ASIC 118 through the engine control unit 121. Asmentioned above, the ASIC 118 will include a memory storage 140 forstoring calibration data, and in some embodiments, storing approximatedcharacteristics for fluids that may undergo sensing by tuning fork 116.

FIG. 2C illustrates another detailed block diagram of the ASIC 118, inaccordance with one embodiment of the present invention. In thisexample, the ASIC 118 shows a number of blocks that may be integratedinto or kept out of, the ASIC 118. Blocks that may be kept outside ofthe ASIC include blocks 175. As a high level diagram, the tuning fork116 is connected to an analog I/O 160. The analog I/O is representativeof blocks 132, 134, and 136, in FIG. 2A above. The analog I/O block 160therefore performs signal conditioning and conversion of the datareceived from the tuning fork 116.

Frequency generator 130, as discussed above, will provide the variablefrequency input signal to the tuning fork 116 through the analog I/O160. Glue logic 162 is provided to integrate together the variouscircuit blocks that will reside on the ASIC 118. As is well known, gluelogic will include signaling lines, interfacing signals, timing signals,and any other circuitry that is needed to provide inputs and outputs toand from the chip that defines the ASIC 118. All such glue logic isstandard and is well known in the art. The ASIC 118 further includesuser defined data (ROM) 140′. As mentioned above, the user-defined data140′ may include calibration data, as well as approximated variable datafor particular fluids that may become fluids under-test. The userdefined data to be stored in this memory can come from any source. Forexample, the data may be obtained from a fluid manufacturer, a tuningfork manufacturer, a contractor party, etc. Still further, the data maybe obtained in the form of a data stream, a database or over a network.

For example, FIGS. 2D and 2E provide exemplary data that may be storedwithin the user-defined data 140′. As shown in FIG. 2D, a tuning fork1.1 (designated as such to emphasize varieties in tuning forks) mayprovide calibration variables, as well as approximated fluidcharacteristics for a particular type of fluid. In the example of FIG.2D, the selected oil type 3 has approximated fluid characteristics fordensity, viscosity, and dielectric constant for a particulartemperature, which is show to be 25° C. As used herein, the term“approximated fluid characteristics” represent starting point values offluid characteristics before the fitting algorithm is started. Thus, thestarting point values are initial values defined from experience,previous tests, or educated guesses. Consequently, the starting pointvalues, in one embodiment, approximate the actual fluid characteristicvalues of the fluid under-test. In this manner, convergence to theactual fluid characteristics can be expedited.

In still another embodiment, it may be possible to start with theapproximated fluid characteristics at some set of fixed values (whichcan be zero, for example). From each fixed value, the fitting algorithmcan move the value until the actual fluid characteristic value isascertained.

Continuing with the example, the approximated fluid characteristics forthe same oil type 3 may have different approximated fluidcharacteristics due to the rise in temperature to 40° C., in FIG. 2E.The calibration variables will also be updated to reflect the values fora particular temperature for the tuning fork 1.1. As new oil typesbecome available to the market, it may be necessary to update theapproximated fluid characteristics for the different temperature rangesso that the user-defined data can be updated in the ASIC 118.

Referring back to FIG. 2C, a digital I/O 142′ is provided to interfacewith a computer 123, and a test I/O interface 164 is provided to enabletesting of the ASIC 118 during design simulation, during test benchtesting, during pre-market release, and during field operation. The ASIC118 will also include a timer 172 to provide coherent operation of thelogic blocks contained in ASIC 118. As mentioned above, the ROM block166, the RAM block 168, the CPU core 170, and the clock 174, canoptionally be included in the ASIC 118 or removed and integrated outsideof the ASIC 118. The ROM 166 will include programming instructions forcircuit interfaces and functionality of the ASIC 118, the RAM 168 willprovide the CPU core 170 with memory space to read and write data beingprocessed by the CPU core 170, and the clock 174 will provide the ASICwith proper signal alignment for the various signals being processed bythe blocks of the ASIC 118.

FIGS. 3A through 3D are provided to illustrate the flexibility of thecomponent blocks contained within the ASIC 118. Groupings 200 a through200 d show that the ASIC 118 can include less or fewer blocks, dependingupon the application and location in which the ASIC will be integrated.For instance, if the ASIC is integrated on a computer in a laboratorysetting, the ASIC may be provided with fewer blocks due to moreprocessing by the host computer. If the ASIC is being integrated into amachine or product tool where no local computer is directly connected tothe product or tool, the ASIC may include more components. However, itshould be understood that the ASIC 118 by the illustration provided bygroupings 200 a through 200 d, can be modularly integrated to includemore or fewer functional blocks.

For completeness, FIG. 3A illustrates an ASIC with only the signalconditioning circuitry 132, and the memory storage 140. Of course, ineach example provided herein, the ASIC will include glue logic andinterfacing logic to interface the resulting ASIC to other circuitry.FIG. 3C illustrates an ASIC with a grouping 200 b that includes thesignal conditioning circuitry 132, the signal detection circuitry 134,and the memory storage 140. FIG. 3B illustrates an ASIC which has agrouping 200 c that includes the frequency generator 130, the signalconditioning circuitry 132, the signal detection circuitry 134, and thememory storage 140. FIG. 3D illustrates a grouping 200 d that includesthe frequency generator 130, the signal conditioning circuitry 132, thesignal detection circuitry 134, the analog-to-digital converter 136, andthe memory storage 140. In each case, as mentioned above, associatedglue logic and digital interfacing logic may be provided to interfacewith the resulting ASIC in accordance with the defined grouping.

FIG. 4 illustrates a circuit diagram 220 for a tuning fork equivalentcircuit 222 and a read-out input impedance circuit 224. The frequencygenerator is coupled to the tuning fork equivalent circuit 222 to aparallel connection of a capacitance Cp as well as a series connectionof a capacitor Cs, a resistor Ro, an inductor Lo, and an equivalentimpedance Z(ω). The read-out impedance circuit includes a parallelresistor Rin and a capacitor Cin. The output voltage is thus representedas Vout. The following equations define the equivalent circuit. Inequation (2), the Vout of the equivalent circuit is defined. Inequations (3) and (4), the impedance Zin and Ztf are derived. Equation(5) illustrates the resulting impedance over frequency Z(ω). As can beappreciated, the voltage Vout, graphed verses the frequency Z(ω),necessitates the determination of several variables.

The variables are defined in equation (1). In operation, the tuningfork's frequency response near the resonance is used to determine thevariables that will define the characteristics of the fluid-under-test.The algorithm that will be used to determine the target fluid under-testcharacteristic parameters will require knowledge of data obtained duringcalibration of a tuning fork. In addition to access to calibration data,the algorithm will also utilize a data fitting process to mergeapproximated variables of the target fluid under-test, to the actualvariable characteristics (i.e., density, viscosity, dielectric constant)for the fluid under-test.

Vout(Co, Cp, Lo, Cs, Ro, Z(ω), A, B, ρ, η, ω, ∈)  (1) $\begin{matrix}{{{Vout}(\omega)} = \frac{{Vo}( {{Zin}(\omega)} }{( {{{Zin}(\omega)} + {{Ztf}(\omega)}} }} & (2)\end{matrix}$  Zin=Rin*(1/ iωCin)(Rin+ 1/ i ωCin)⁻¹  (3)Z _(tf)=(1/iωCp)(Ro+1/iωCs+iωLo)  (4)(1/iωCp+Ro+1/iωCs+iωLo)⁻¹ Z(ω)=Aiωp+B*(ωρη)^(1/2)(1+i)  (5)∈_(measured) =a+k*Cp _((measured))  (6)$\begin{matrix}\begin{matrix}{ɛ_{measured} = {\lbrack {ɛ_{cal} - {( {ɛ_{cal} - 1} )*\lbrack {{Cp}_{cal}/( {{Cp}_{cal} - {Cp}_{o}} )} \rbrack}} \rbrack +}} \\{\lbrack {{Cp}_{({measured})}*\lbrack {( {ɛ_{cal} - 1} )/( {{Cp}_{cal} - {Cpo}_{({vacuum})}} )} \rbrack} \rbrack}\end{matrix} & (7)\end{matrix}$  a=[∈ _(cal)−(∈_(cal)−1)*[Cp _(cal)/(Cp _(cal) −Cp_(o))]  (8)k=[(∈_(cal)−1)/(Cp _(cal) −Cpo _((vacuum)))]  (9)Cp_((measured)) is a function of “k”  (10)

In the circuit, it is assumed that C_(S), R_(O), L_(O) are equivalentcharacteristics of a preferred resonator in a vacuum, C_(p) is theequivalent parallel capacitance in a particular fluid under-test, ρ isthe fluid density, η is fluid viscosity, ω is oscillation frequency. Cpis a function of k, as shown in equations (6) through (10). The constant“k” is, in one embodiment, a function of the tuning fork's geometry, andin one embodiment, defines the slope of a curve plotting (Cp_(measured),Cp_(cal), and Cp_(vaccum)) verses (∈_(measured), ∈_(cal), and∈_(vacuum)), respectively. In a physical sense, the constant “k” is afunction of the tuning fork's geometry, the geometry of the tuningfork's electrode geometry, the tuning fork's packaging (e.g., holder)geometry, the material properties of the tuning fork, or a combinationof any of the above factors. The resulting value of Cp will be used todetermine the dielectric constant E as shown by the equations.

Further, based on the below defined equations, it can be seen thatviscosity and density can be de-convoluted by the following:$\begin{matrix}{{Z(\omega)} = {{{Ai}\quad\omega\quad\rho} + {B\sqrt{{\omega\rho}\quad\eta}( {1 + i} )}}} \\{{Z(\omega)} = {{i\quad{\omega\Delta}\quad L} + {\Delta\quad Z\sqrt{\omega}( {1 + i} )}}} \\{{{\Delta\quad L} = {A\quad\rho}},{{\Delta\quad Z} = {B\sqrt{\rho\eta}}}}\end{matrix}$

For some sensors, the value of C_(p measured) is typically on the orderof about 1 to 3 orders of magnitude greater than the value of C_(s).Accordingly, in order to improve the ability to measure Z(ω), desirablytrimming circuitry is employed as part of or in association with thesignal conditioner, such as (without limitation), one or a combinationof the illustrative trimming circuits of FIG. 6A, 6B, or 6D.

FIG. 5 shows a graph 230 that plots voltage out (Vout) versus frequency(ω). As shown, the actual tuning fork response signal may produce asignal 232 that spans a particular frequency range. The frequency rangewill exhibit the signal having a resonance response that is indicativeby the wiggle in the signal 232. The amplitude of the wiggle in thesignal 232 may be in the range of about 1 mV to about 10 mV. However,the actual signal 232 produced by the tuning fork 116 will be at asignal offset that can be in the range of about 100 to about 1,000 mV,depending on the tuning fork characteristics and the fluid under-test.

In order to more efficiently process the signal being received from thetuning fork, the signal 232 is signal conditioned to eliminate or reducethe signal offset and thus, increase the dynamic range of the signalproduced by the tuning fork. Thus, the data being analyzed can be moreaccurately processed. The conditioned signal is shown as signal 232′ inFIG. 5. Exemplary techniques for conditioning the signal 232 to producesignal 232′ will be illustrated with reference to FIGS. 6A and 6D below.

FIG. 6A shows a circuit 300 a where an amplifier 310 receives input fromthe tuning fork 116, and input from a capacitor 316, in accordance withone embodiment of the present invention. The capacitor 316 is providedto assist in the signal conditioning that shifts the signal 232 of FIG.5 to eliminate/reduce the signal offset and produce signal 232′. Asshown, the frequency generator will provide the frequency stimulus tothe tuning fork 116, and also to the capacitor 316.

The output from the capacitor 316 is provided to the negative terminalof the amplifier 310 and the output of the tuning fork 316 is providedto the positive terminal of the amplifier 310. The amplifier 310 willtherefore provide an amplified signal which has been shifted due to thecapacitance provided by capacitor 316, to a signal detection circuit(SDC) 134. The signal detection circuit will detect the phase andamplitude of the signal being output by the amplifier 310, and thenprovide the output to an analog-to-digital converter 136.

Capacitor 316, although shown to be variable, is in one embodiment,fixed to a particular level depending upon the shift necessary (oranticipated) to condition the received signal from the tuning fork 116.In one preferred embodiment, the tuning fork 116 may itself beconfigured to include the capacitor 316. An example where the capacitor316 is integrated to the tuning fork 116 is shown in FIG. 7 below.

FIG. 6B illustrates a circuit 300 b in which the tuning fork provides aninput to an amplifier 310. The negative terminal of amplifier 310 is, inone exemplary embodiment, connected to ground. The output of theamplifier 310 is shown provided to the signal detection circuitry 134.In this embodiment, the signal detection circuitry 134 may be a rootmeans squared (RMS) circuit that is configured to rectify the analogsignal received from the amplifier 310. The output of the signalconditioning circuit 134 will then be output to the analog-to-digitalconverter 136, as in FIG. 6A.

In this embodiment, a digital-to-analog (DAC) converter 318 is providedto generate a compensating signal 317 a to the analog-to-digitalconverter (ADC). The compensating signal will assist in providing theshift necessary to eliminate the signal offset as discussed withreference to FIG. 5. In an alternative embodiment, the digital-to-analogconverter 318 will provide signal 317 directly to the signal detectioncircuit 134, as opposed to the analog-to-digital converter, and thisoption is illustrated by way of a dashed line 317 b. Thedigital-to-analog converter 318 is, in this embodiment, designed toreceive control from the digital logic control 142 as shown in FIG. 2A.In still another modification, the circuit 300 b may be designed toexclude the signal detection circuit 134, and therefore provide theoutput of the amplifier 310 directly to the analog-to-digital converter136 through a signal line 319. In such a case, the digital-to-analogconverter 318 will provide its compensating signal directly to theanalog-to-digital converter by way of signal line 317 a. In thisembodiment, the analog-to-digital converter 136 will be capable ofdetecting the signal and its appropriate phase and amplitude, thuseliminating the need for a signal detection circuit 134.

FIG. 6C illustrates a graph of voltage output versus frequency in whichan analog signal is output from the tuning fork. The analog signal, inone embodiment, will be processed through the signal detection circuit(the RMS function of FIG. 6B), to generate a rectified signal 360 a. Therectified signal is then conditioned by shifting it down to thuseliminate/minimize the signal offset by use of the digital-to-analogconverter 318 of FIG. 6B. The resulting signal 360 a′ will thereforehave a wider dynamic range which can be more efficiently processed bythe digital circuitry that will apply the algorithm for determining thecharacteristics of the fluid under-test.

FIG. 6D illustrates yet another embodiment in which a circuit 300 cprovides signal conditioning before performing the analog-to-digitalconversion in block 136. In this example, the tuning fork 116 and thecapacitor 316, are couple to a differential amplifier 310. Thedifferential amplifier 310 is capable of generating an amplified signalthat is well represented of variables associated with density andviscosity, however, the capacitance of the fluid under-test (Cp) is avalue that may be eliminated during the processing by the differentialamplifier 310. For this reason, a summation amplifier 312 may beprovided, and is connected 311 a by way of a resistor to the negativeterminal that couples to the capacitor 316, to thus produce datarepresentative of Cp. In another embodiment, an additional connectionmay be made to the output of the tuning fork and the positive input ofthe differential amplifier 310. Thus, connection 311 b will provideadditional sensitivity and data for generating an appropriate Cp for thefluid under-test.

The analog signals coming from both the summation amplifier 312 and adifferential amplifier 310 will be provided to the signal detectioncircuit 134, which will identify the appropriate phase and amplitude forthe signals being output from the amplifiers. The signal detectioncircuit 134 will then output the data to the analog-to-digital converter136.

FIG. 7 illustrates a tuning fork 116′ in which a capacitor 316 has beenintegrated directly onto the surface of the tuning fork 116′. Tuningfork 116′, as defined above, will include electrodes 116 a and thecapacitor 316 will include capacitor electrodes 316 a that are capableof reading a capacitate charge to enable the tuning fork to itself,provide the offset necessary to condition the signal and provide theshift described with reference to FIG. 5. Thus, the tuning fork itselfwill provide the necessary elimination/reduction of the signal offset.The capacitor 316, in one embodiment, will be trimmed/set by themanufacturer to provide a capacitate value that is approximately capableof providing the necessary offset. In another embodiment, the capacitorcan be of a form that will enable trimming after manufacturing.

One preferred tuning fork resonator of the present invention has one ormore tines including a piezoelectric material and at least one electrode(or suitable structure for receiving the electrode) connected to thepiezoelectric material. A performance-tuning material or otherfunctionality optionally may also be included on the base material.

The use of a metal is most preferred for the electrodes. However, otherconductive materials may also be employed, such as conductive polymers,carbon or otherwise. Preferred metals are pure metals or alloysincluding a metal selected from gold, platinum, silver, chromium,aluminum or mixtures thereof. Other noble or transition metals may alsobe employed.

The base materials of the resonators of the present invention preferablyare selected from at least one type of device of piezoelectricmaterials, electrostrictive materials, magetostrictive materials,piezoresistive materials, elasto-optic materials, anisotropic materials,or combinations thereof. By way of example, the particular material maybe a metallic material, a crystalline material, a ceramic material or acombination thereof. Examples of suitable materials include, withoutlimitation, quartz, lithium niobate, zinc oxide, lead zirconate titanate(PZT), gallo-germanates (e.g., Langasite (La₃Ga₅SiO₁₄), Langanite, orLangatate), diomignite (lithium tetraborate), bismuth germanium oxide orcombinations thereof. The preferred base materials may be undoped ordoped with art-disclosed dopants.

Preferably the dimensions of the resonators for use in accordance withthe present invention are such that the total volume of the resonatorincluding the performance-tuning material is less than about 75 mm³,more preferably less than about 50 mm³, still more preferably less thanabout 25 mm³, and even still more preferably less than about 15 mm³. Onepreferred resonator has tines that do not exceed about 15 mm in itslongest dimension, and more preferably is smaller than about 8 mm in itslongest dimension. A preferred resonator has a thickness no greater thanabout 2 mm, and more preferably no greater than about 1 mm. By way ofexample, without limitation, one illustrative resonator is about 0.5×3×5mm in dimension. Of course, larger resonators may also be employed. Inone embodiment, a size of the tuning fork 116 is smaller than a wavelength of an acoustic wave.

Examples of particularly preferred performance-tuning materials includeone or a combination of two or more materials selected from the groupconsisting of polymers, ceramics, diamond, diamond-like carbon (e.g.,Diamonex® DLC), and combinations thereof. For example, preferredperformance-tuning materials might include one or a combination of twoor more materials selected from the group consisting of fluoropolymers,silicones, polyolefins, carbides, nitrides, oxides, diamond,diamond-like carbon, and combinations thereof; and even moreparticularly might include one or a combination of two or more materialsselected from the group consisting of polytetrafluoroethylene,fluorosilicone, polyethylene (e.g., high density polyethylene),polypropylene (e.g., high density polypropylene), silicon carbide,silicon nitride, diamond, diamond-like carbon, and combinations thereof.It is also possible that a material selected from the above identifiedexamples of base materials may be employed as a performance tuningmaterial.

FIG. 8 illustrates a flowchart diagram 400 depicting method operationsperformed to calibrate a tuning fork and obtaining variablescharacterizing a tuning fork, in accordance with one embodiment of thepresent invention. The method begins at operation 402 where a tuningfork sensor is provided. As mentioned above, the tuning fork sensor ispreferably designed to be inserted into a fluid under-test to determineproperties of the fluid. In one embodiment, the tuning fork sensor willbe provided with electrodes to enable application of a variablefrequency input signal over a predetermined frequency range to obtain afrequency-dependent resonator response. The method now moves tooperation 404 where a first calibration to determine a first set ofvariables characterizing the tuning fork, is performed. The firstcalibration includes subjecting a tuning fork to vacuum or air todetermine the response of the tuning fork and calibrate it against aknown resonance frequency response.

FIG. 11A illustrates an example of a known frequency response of thetuning fork in vacuum or air as shown by signal 462. Starting from anapproximated signal 464 for the tuning fork in air, a fitting algorithmis executed to fit the approximated signal 464 to the signal 462. Inperforming this first calibration, it is possible to ascertain variablessuch as the inductance (Lo), the capacitance (Cs), the resistance (Ro),and the parallel capacitance (Cp) of the tuning fork in the medium. Asthe tuning fork is subjected to vacuum or air the impedance of thefluid, Z(ω) will be equal to zero.

Accordingly, the first calibration will generate the first set ofvariables characterizing the actual tuning fork itself, as shown in thefirst calibration in FIG. 11A. Returning to FIG. 8, the method thenmoves to operation 406 where a second calibration in a known fluid isperformed to determine a second set of variables. The second calibrationwill use the determined first set of variables from the firstcalibration. Reference is now made to FIG. 11B in which a secondcalibration is performed. In the second calibration, the frequencyresponse will be provided for a known fluid as shown by signal 472.Beginning with an approximated signal for the known fluid 474, thecalibration will take place such that signal 474 fits the known fluidsignal 472. In performing the curve fitting operation, the secondcalibration will use the first calibration variables from FIG. 11A, toobtain the second set of variables which include A, B, and k. In oneembodiment, the known fluid used in the second calibration willpreferably be a volatile fluid so that contamination of the tuning forkwill be maintained at a minimum. That is, it is a desire prevent thetuning fork from collecting or building up residues on the tines, beforeactual fluid under-test variable determinations are made using the sametuning fork. In one example, the known fluid may be carbon tetrachloride(CCl₄), alcohol, fluorinated solvents, ethanol, methanol, toluene,menthol ether ketone, hexane, heptane, isopropyl alcohol (IPA), etc.Still another calibration fluid may be deionized water (DIW) or otherfluids that will not leave or only leave minimal residues on the tuningfork.

Returning again to FIG. 8, once the second calibration has beenperformed in operation 406, the method will move to operation 408 wherethe first set of variables and the second set of variables are stored inmemory for functional use of the tuning fork in sensing characteristicsof a fluid to be tested. In one embodiment, the first set of variablesand the second set of variables are stored in the memory storage 140 orthe user-defined data ROM 140′, as discussed with reference to FIGS. 2Band 2C. Broadly speaking, the first calibration and the secondcalibration data will be performed on a tuning fork for a range oftemperatures as shown in FIGS. 2D and 2E. The range of temperatures mayvary between about 1 Kelvin and about 1000 Kelvin. In anotherembodiment, the range may be between about 77 Kelvin and about 600Kelvin, and in still another embodiment, the range may be between about233 Kelvin and about 423 Kelvin. Such ranges will vary depending on theapplication. These calibration variables from the first calibration andthe second calibration, will therefore be stored in memory and can berecalled by the ASIC when processing a fluid under-test to ascertaincharacteristics of the fluid under-test, such as the density, viscosity,and the dielectric constant. In still another embodiment, thecalibration variables may be stored on a removable storage media. Whenthe calibration variables are stored on a removable storage media, thecalibration data will be linked to a particular tuning fork.Accordingly, when a tuning fork is supplied to an end user, the end usermay also be provided with the removable storage media (e.g., card, chip,memory stick, etc.) so that the appropriate calibration variables can beloaded onto or accessed by the ASIC for operation of the tuning fork. Bystoring the calibration variables in a removable storage media, it isalso possible to continually update and refine the calibration variablesfor new tuning forks, and also provide the latest calibration data toend users when new tuning forks are provided for sale.

Still further, a particular embodiment may include the sale of aparticular tuning fork and calibration variables for the tuning fork asa package. The calibration variables may also be stored on a magneticcard and the card can then be inserted into a computer or the localmachine user interface by a technician to load the current calibrationdata for a particular tuning fork that is being installed in aparticular machine. From time to time, it will be possible to update thecalibration data for a tuning fork through the local machine userinterface, by a technician, for example. Updates can also be provided tolocal electronics over a wireless link, over the Internet, etc. In oneembodiment, the calibration data can be compactly stored, and providedin digital form is as little space as 64 bytes. Of course, the data sizecan increase or decrease depending on the needs.

FIG. 9 illustrates a flowchart diagram 420 in which an ASIC is used tocontrol activation of a tuning fork and also process the response fromthe tuning fork to enable communication of the response data in digitalform. The method begins at operation 422 where a tuning fork sensor isprovided. Once the tuning fork sensor has been provided, the methodmoves to operation 424 where the tuning fork sensor is applied into afluid under-test. Applying the tuning fork sensor into a fluidunder-test may include submerging a portion of the tuning fork (i.e., atleast a portion of the tines) into the fluid under-test to enable thetuning fork to resonate within the fluid to be tested.

Once the tuning fork sensor has been applied to the fluid under-test,the method moves to operation 426. In operation 426, stimulus is appliedto the tuning fork sensor. As mentioned above, the stimulus will be afrequency input signal that is varied over a frequency range and appliedto the tuning fork sensor, to obtain a frequency-dependent resonatorresponse. Preferably, the applied frequency will be less than about 100kHz. The ASIC will then receive an analog signal from the tuning forksensor while the tuning fork is in the fluid under-test in operation428. Once the ASIC receives the analog signal from the tuning forksensor, the method moves to operation 430, where the analog signal isprocessed into digital form.

As mentioned above, the ASIC will preferably include signal conditioningcircuitry for receiving the analog signal, signal detection circuitryfor detecting components of the signal being obtained from the tuningfork sensor, and an analog-to-digital converter to move the analogsignal data into digital form. The method now moves to operation 432where the digital form of the received analog signal is processed toidentify characteristics of the fluid under-test.

In one embodiment, the processing of the digital form received from theanalog signal, may also be performed by the ASIC in block 425. In analternative embodiment, as mentioned above, the processing of thedigital form may be performed outside of the ASIC as shown in FIG. 2B.In either embodiment, the digital form is then processed to identifycharacteristics of the fluid under-test. As will be discussed withreference to FIG. 11C, the characteristics of the fluid under-test beingidentified may include density, viscosity, and the dielectric constantof the fluid under-test. Once the characteristics have been identifiedin operation 432, the method will move to operation 434 where theidentified characteristics are communicated to a predefined receivingunit. The predefined receiving unit may include a computer of a vehicle,a computer in a laboratory, a storage device, a remote computerreceiving data over the Internet (by connected wires or wireless), orany other receiving unit desiring to receive information regarding thefluid under-test. Once the identified characteristics have beencommunicated to the predefined receiving unit, the method will end.

FIG. 10 illustrates a flowchart diagram 440 in which a curve fittingalgorithm is performed in block 445, in accordance with one embodimentof the present invention. As mentioned above, the curve fittingalgorithm is designed to fit approximated signal data for a particularfluid to an actual signal received from a fluid under-test as shown inFIG. 11C. The curve fitting algorithm is also applied to the process forobtaining the first calibration data and the second calibration data, inaccordance with one embodiment.

The method begins at operation 442 where the first and second set ofvariables determined during calibration are loaded into memory. Asmentioned above, the calibration data may be stored either on the ASICitself in memory, or may be stored off the ASIC on a host computer oreven on a removable storage media such as a magnetic card or the like.As mentioned above, the first and second set of variables determined toa calibration are most likely temperature dependent, and the calibrationdata will be identified for the particular temperature being sensedduring the fluid under-test operation.

The method now moves to operation 444 where characteristics of the fluidunder-test are read to obtain data for a signal representative of thefluid under-test. Reference is now made to FIGS. 2D and 2E wheredifferent oil types are provided with approximated fluidcharacteristics. For example, oil type 3 will include approximated fluidcharacteristics for density, viscosity, and the dielectric constant.Each of these approximated fluid characteristics along with thecalibration variables, will be tied to a particular temperature. As thetemperature rises, e.g., as shown in FIG. 2E, the values for theapproximated fluid characteristics may also change, therefore definingslightly different values for the density viscosity and dielectricconstant.

Once the data has been obtained from storage by way of a fetch, lookupor the like, these approximated fluid characteristic values are used toproduce a signal representative of the fluid under-test. Reference isnow made to FIG. 11C, where the signal that is representative of thefluid under-test is shown as signal 484. As can be seen, signal 484 isapproximately similar to the signal provided by the actual fluidunder-test, and shown as signal 482. In this example, the tuning forkhas been inserted into the fluid under-test, and the frequency responseof the tuning fork will produce the signal 482, as shown in FIG. 11C.Since the fluid under-test produced an actual signal 482, curve fittingthe approximated signal that is representative of the fluid under-test,i.e., signal 484, will produce the actual fluid characteristic data forthe fluid under-test signal 482. The result is that the fluid under-testfluid characteristic data, including the density, viscosity, anddielectric constant, will be generated for the actual fluid under-test.

Returning to FIG. 10, once the data is obtained for the signal that isrepresentative of the fluid under-test, the method will move tooperation 446. Operations 446, 448, and 450 will be part of a curvefitting algorithm defined in block 445. In operation 446, anapproximated signal for the fluid under-test is generated. Theapproximated signal for the fluid under-test is shown in FIG. 11C assignal 484. The method will then move to operation 448 where a fittingalgorithm is applied to fit the approximated signal to the actual signalfor the fluid under-test. As mentioned above, this involves applying analgorithm that will merge the approximated signal 484 values onto thefluid under-test signal 482.

The curve fitting algorithm is a repetitive algorithm that willcontinuously operate until a suitable or best curve fitting result isproduced. Thus, the method will move to decision operation 450, where itis determined whether the fit is acceptable. If the fit is notacceptable, meaning that the approximated signal 484 is not sufficientlyclose to the fluid under-test signal 482, the method will return tooperation 446. In operation 446, the new updated approximated fluidcharacteristic variables are updated to the formula to then producingnew approximated signal 484 that may be closer to the fluid under-test.Again, the method moves to operation 448 where the fitting algorithm isperform to again attempt to merge the approximated signal 484 onto thefluid under-test signal 482 as shown in FIG. 11C.

This method will continue until an acceptable curve fitting degree hasbeen reached. If successive loops have occurred and the curve fittingdoes not improve, it is possible for the signal to be acceptable and themethod will move to operation 452. In a preferred embodiment, the curvefitting algorithm will use a simplex equation curve fitting algorithm toassist in merging the approximated signal to the actual signal receivedfrom the fluid under-test. In a more preferred embodiment, the simplexequation will utilize operations to minimize the least squares values ofa theoretical model. An example algorithm that may be used may include adownhill simplex algorithm for multidimensional applications. Thealgorithm is defined in a book entitled “The Art of ScientificComputing,” having authors William H. et al. copyright date 1988.Specific pages of interest include, pages 305-309, chapter 10.4,entitled “Downhill Simplex Method in Multidimensions.” This book isincorporated herein by references for all purposes. Of course, it shouldbe understood that other fitting algorithms may also be used, so long asthe function of “fitting” is achieved.

The method will then move to operation 452 where the actual determinedcharacteristic data for the fluid under-test is output to produce theascertained density, viscosity, and dielectric constant for theparticular fluid under-test.

FIGS. 11A through 11B have been discussed above with reference to thecurve fitting operations. Specifically, FIG. 11A illustrates a curvefitting operation that takes place in vacuum or air to obtain the firstset of variables by curve fitting an approximated signal for vacuum orair 464 to an actual vacuum or air signal 462. FIG. 11B shows the curvefitting operation performed to merge an approximated signal 474 of aknown fluid, to the actual response of the known fluid 472. By mergingthe approximated signal 474 to signal 472, which is the actual signalreceived from the known fluid, it is possible to obtain the second setof calibration variables A, B, and k. Finally, FIG. 11C illustrates thecurve fitting operation that is performed during actual use of a tuningfork to obtain characteristic variables of a particular fluidunder-test.

FIG. 12 illustrates a flowchart diagram 490, depicting the basicfunctional process operations performed by an ASIC 118 to produce fluidparameters for a fluid under-test using a tuning fork, in accordancewith one embodiment of the present invention. The method begins atoperation 492 where the first set of variables that were obtained usinga curve fitting algorithm are fetched from storage. The method thenmoves to operation 494 where the second set of variables that wereobtained using the first set of variables and the curve fittingalgorithm are also fetched from storage. As mentioned above, the secondset of variables will define calibration variables for a particulartuning fork. The calibration variables will be stored either directly onthe ASIC, off the ASIC, or on some storage medium. Once the calibrationvariables have been obtained, the processor that is either part of theASIC or in communication with the ASIC, will produce fluid parametersfor the fluid under-test using the first set of variables, the secondset of variables, and the curve fitting algorithm in operation 496.

Examples of the tuning fork sensor of the present invention can be foundin U.S. Provisional Patent Application No. 60/419,404, which isincorporated by reference herein. In summary, the tuning fork resonatoris a mechanical piezoelectric resonator that is capable of measuringphysical and electrical properties, such as the viscosity, density,dielectric constant, and the conductivity of a sample fluid.

The tuning fork resonator should be broadly construed to include anyresonator that can oscillate in a fluid. Other example resonatorstructures may include tridents structures, cantilever structures,torsion bar structures, unimorph structures, bimorph structures,membrane resonator structures or combinations thereof.

In a most basic configuration, the sensing system of the presentinvention is configured with a sensor such as a mechanical resonator, aprocessor and a user interface to inform the user of a level and/orcondition of the fluid. In this embodiment, the sensor receives anexcitation signal from a signal generator, causing the sensor toresonate. The resonance of the sensor is proportionally related to theviscosity of the fluid, which is directly correlated to the type andpresent state of the fluid condition. The resulting resonance istransmitted via a generated output signal to a processor, which modifiesthe signal for analysis and compares it with a known value so as todetermine the present state of the fluid.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. For example, though a feature of an embodiment maydescribed particularly in the context of engine oil, it is not to belimited to that application. The principles of the present inventionhave widespread application for other automotive vehicle fluids and inapplications outside automotive applications (e.g., in devices foranalyzing a property of a fluid flowing in a conduit in an oil field; indetectors associated with flow injection analysis instruments; inmicrobalances; in systems for high throughput research and screening; orotherwise). Accordingly, the present embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalents of the appended claims.

1. A system for sensing characteristics of a fluid, comprising: a tuningfork configured to be at least partially submerged in a fluidunder-test; and an application specific integrated circuit (ASIC), theASIC including, analog input/output circuitry for providing stimulus tothe tuning fork and receiving a response signal from the tuning fork;conditioning circuitry for reducing analog signal offsets in theresponse signal; signal detection circuitry for identifying amplitudedata of the response signal; analog-to-digital conversion circuitry forconverting the detected amplitude data into digital form; and memory forholding user defined data, wherein the digital form of the responsesignal is processed in conjunction with the user defined data togenerate fluid characteristics of the fluid under-test.
 2. A system forsensing characteristics of a fluid as recited in claim 1, wherein theuser defined data includes at least one of calibration data andapproximated fluid characteristics of the fluid under-test.
 3. A systemfor sensing characteristics of a fluid as recited in claim 2, furthercomprising: a temperature sensor, the temperature sensor designed toread a temperature next to the tuning fork, the temperature readingbeing utilized to select a temperature specific set of calibration dataand approximated fluid characteristics of the fluid under-test.
 4. Asystem for sensing characteristics of a fluid as recited in claim 2,wherein one or both of the calibration data and approximated fluidcharacteristics of the fluid under-test are capable of being stored onone of a memory card, a memory stick, a hard drive, an optical disc, andon a network storage.
 5. A system for sensing characteristics of a fluidas recited in claim 1, wherein the ASIC is in communication with aprocessor, the processor being configured to process a fitting algorithmto ascertain the fluid characteristics of the fluid under-test.
 6. Asystem for sensing characteristics of a fluid as recited in claim 5,wherein the ASIC further includes an integrated CPU, the CPU beingconfigured to process a fitting algorithm to ascertain the fluidcharacteristics of the fluid under-test.
 7. A system for sensingcharacteristics of a fluid as recited in claim 6, wherein the fittingalgorithm implements a simplex equation to minimize least squaresvalues.
 8. A system for sensing characteristics of a fluid as recited inclaim 5, wherein the fitting algorithm implements a simplex equation tominimize least squares values.
 9. A system for sensing characteristicsof a fluid as recited in claim 1, wherein the ASIC is coupled to localmachine electronics of a machine.
 10. A system for sensingcharacteristics of a fluid as recited in claim 9, wherein the machine isan automobile and the fluid under-test is engine oil.
 11. A system forsensing characteristics of a fluid as recited in claim 10, furthercomprising: a local machine user interface for providing one of analogand digital data regarding the fluid characteristics of the fluidunder-test.
 12. A system for sensing characteristics of a fluid asrecited in claim 9, wherein the local machine electronics includesengine control electronics.
 13. A system for sensing characteristics ofa fluid as recited in claim 1, wherein the ASIC includes digital logiccontrol for interfacing components internal to the ASIC to componentsexternal to the ASIC.
 14. A system for sensing characteristics of afluid as recited in claim 13, wherein the ASIC is integrated intoelectronics of one of a motor, a measurement while drilling tool, alogging while drilling tool, an exploration and production well loggingtool, a printed circuit board, and a computer motherboard.
 15. A systemfor sensing characteristics of a fluid as recited in claim 1, whereinthe generated generate fluid characteristics of the fluid under-test aredisplayed on a display monitor.
 16. A system for sensing characteristicsof a fluid as recited in claim 1, wherein the memory is rewritable. 17.A system for sensing characteristics of a fluid as recited in claim 1,wherein the ASIC further comprises: glue logic for interfacingcomponents of the ASIC.
 18. A system for sensing characteristics of afluid as recited in claim 1, wherein the ASIC further comprises: adigital I/O for interfacing with a computer.
 19. A system for sensingcharacteristics of a fluid as recited in claim 1, wherein the ASICfurther comprises: a ROM; a RAM; a CPU; and a clock.
 20. A system forsensing characteristics of a fluid as recited in claim 1, wherein theASIC further comprises: a timer.
 21. A system for sensingcharacteristics of a fluid as recited in claim 1, wherein the tuningfork has an integrated capacitor.
 22. A system for sensingcharacteristics of a fluid as recited in claim 21, wherein the capacitoris integrated on the tuning fork.
 23. A system for sensingcharacteristics of a fluid as recited in claim 22, further including, acapacitor coupled to an input of the differential amplifier.
 24. Asystem for sensing characteristics of a fluid as recited in claim 1,wherein the signal conditioning circuitry includes, a differentialamplifier for receiving an input from tuning fork, the input from thetuning fork being the response signal; and a capacitor coupled to aninput of the differential amplifier.
 25. A system for sensingcharacteristics of a fluid as recited in claim 1, wherein the signalconditioning circuitry includes, a differential amplifier for receivingan input from tuning fork, the input from the tuning fork being theresponse signal; and a digital-to-analog converter for providingcompensation to one of the signal detection circuitry and theanalog-to-digital converter.
 26. A system for sensing characteristics ofa fluid as recited in claim 1, wherein the signal conditioning circuitryincludes, a differential amplifier for receiving an input from tuningfork, the input from the tuning fork being the response signal; acapacitor coupled to an input of the differential amplifier; and asummation amplifier, the summation amplifier coupled between thedifferential amplifier and the capacitor.
 27. A circuit for determiningcharacteristics of a fluid under-test, comprising: analog-to-digitalprocessing circuitry for interfacing with a sensor and host electronics,the analog-to-digital processing circuitry including, a frequencygenerator for providing stimulus to the sensor; conditioning circuitryfor receiving a response signal from the sensor and reducing analogsignal offsets in the response signal; signal detection circuitry foridentifying amplitude data of the response signal; analog-to-digitalconversion circuitry for converting the detected amplitude data intodigital form; and memory capable of holding data characterizing thesensor, wherein the digital form of the response signal is processed togenerate fluid characteristics of the fluid under-test.
 28. A circuitfor determining characteristics of a fluid under-test as recited inclaim 27, wherein the data characterizing the sensor includescalibration data.
 29. A circuit for determining characteristics of afluid under-test as recited in claim 27, wherein the memory furtherbeing capable of holding approximated characteristic data of the fluidunder-test.
 30. A system for determining characteristics of a fluid asrecited in claim 27, wherein the analog-to-digital processing circuitryis incorporated into an application specific integrated circuit (ASIC).31. A system for determining characteristics of a fluid as recited inclaim 27, wherein the signal conditioning circuitry and the memory areintegrated into an application specific integrated circuit (ASIC).
 32. Asystem for determining characteristics of a fluid as recited in claim27, wherein the signal conditioning circuitry, the signal detectioncircuitry, and the memory are integrated into an application specificintegrated circuit (ASIC).
 33. A system for determining characteristicsof a fluid as recited in claim 27, wherein the signal conditioningcircuitry, the signal detection circuitry, the frequency generator, andthe memory are integrated into an application specific integratedcircuit (ASIC).
 34. A system for determining characteristics of a fluidas recited in claim 27, wherein the signal conditioning circuitry, thesignal detection circuitry, the frequency generator, theanalog-to-digital conversion circuitry and the memory are integratedinto an application specific integrated circuit (ASIC).
 35. A system fordetermining characteristics of a fluid as recited in claim 34, whereinthe ASIC further includes an integrated processor.
 36. A system fordetermining characteristics of a fluid as recited in claim 35, whereinthe integrated processor is one of a CPU, a microprocessor core, amicrocontroller, a state machine, a digital signal processor.
 37. Asystem for determining characteristics of a fluid as recited in claim27, wherein the signal detection circuitry includes one of an RMSdetector and a synchronous detector.
 38. A system for determiningcharacteristics of a fluid as recited in claim 27, wherein the sensor isa mechanical resonator.
 39. A system for determining characteristics ofa fluid as recited in claim 38, wherein the mechanical resonator is atuning fork.
 40. A system for determining characteristics of a fluid asrecited in claim 27, wherein the sensor is a tuning fork with anintegrated capacitor.
 41. A system for determining characteristics of afluid as recited in claim 28, wherein the ASIC is integrated with thesensor.
 42. A system for determining characteristics of a fluid asrecited in claim 28, wherein the ASIC is integrated in vehicleelectronics.
 43. A system for determining characteristics of a fluid asrecited in claim 28, wherein the fluid under-test is vehicle fluid. 44.A system for determining characteristics of a fluid as recited in claim28, wherein the vehicle fluid is oil.
 45. A method for interfacing witha mechanical sensor to obtain characteristics of a fluid under-test, themechanical sensor being at least partially submerged in the fluidunder-test, the method comprising: applying a variable frequency signalto the sensor; receiving a frequency response from the sensor;conditioning the frequency response; detecting signal components of thefrequency response; converting the frequency response to digital form,the digital form being representative of the frequency response receivedfrom the sensor; fetching first calibration variables from memory, thefirst calibration variables defining physical characteristics of thesensor; fetching second calibration variables from memory, the secondcalibration variables defining characteristics of the sensor in a knownfluid; and processing the digital form of the response received from thesensor when in the fluid under-test along with the fetched first andsecond calibration variables, the processing implementing a fittingalgorithm to produce fluid characteristics of the fluid under-test. 46.A method for interfacing with a mechanical sensor to obtaincharacteristics of a fluid under-test as recited in claim 45, whereinthe fluid characteristics produced for the fluid under-test includedensity, viscosity and dielectric constant values.
 47. A method forinterfacing with a mechanical sensor to obtain characteristics of afluid under-test as recited in claim 45, wherein the fitting algorithmexecutes a simplex equation to minimize least squares.
 48. A method forinterfacing with a mechanical sensor to obtain characteristics of afluid under-test as recited in claim 45, wherein the first calibrationof the sensor is performed in one of air and vacuum.
 49. A method forinterfacing with a mechanical sensor to obtain characteristics of afluid under-test as recited in claim 45, wherein known fluid is avolatile fluid.
 50. A method for interfacing with a mechanical sensor toobtain characteristics of a fluid under-test as recited in claim 45,wherein the first calibration and the second calibration utilize thefitting algorithm.
 51. A method for interfacing with a mechanical sensorto obtain characteristics of a fluid under-test as recited in claim 45,wherein the method operations are executed using circuitry.
 52. A methodfor interfacing with a mechanical sensor to obtain characteristics of afluid under-test as recited in claim 45, wherein some of the circuitryis part of an application specific integrated circuit (ASIC).